Nanocutting Process Research Articles

Improvement of dimensional accuracy and surface quality of microlens arrays by a profile cutting method

Single-point diamond cutting is an efficient method to fabricate microlens arrays (MLAs). However, machining MLAs at the microscale with high dimensional accuracy and a smooth surface finish is a difficult task. In this study, a method of profile cutting is proposed to machine MLAs on electroless nickel–phosphorus (Ni–P) plating. To improve the dimensional accuracy of MLAs, a precision tool setting method is introduced, via which the precision of MLA sag can be controlled to within 20 nm. In addition, the formation mechanism of corrugation defects is studied via a finite element (FE) simulation of the wedge nano-cutting process and a cutting experiment of concentric ring grooves. By optimizing the tool settings and the machining parameters, high-quality MLAs with apertures of Φ100 μm can be created.

Molecular dynamics simulation study of interaction mechanism between grain boundaries and subgrain boundaries in nano-cutting

In nano-cutting, grain boundaries with complex network structures hinder the movement of defects like subgrains in nanocrystalline materials, affecting the surface generation process and mechanical properties of the machined materials. In this work, the interaction mechanism between the grain boundaries and the subgrain boundaries in nano-cutting is investigated by molecular dynamics (MD) simulations. The results show that the extrusion action between the grain boundaries and the cutting tool causes the periodic formation and annihilation of the subgrains in nano-grains. The interactions between the grain boundaries and the subgrains lead to continuous pile-up formation, obvious stresses accumulation, elastic recovery of the machined surface, and periodic oscillation of processing force. This study will be helpful for designing the nano-cutting process to get better surface quality and mechanical properties of nanocrystalline materials.

Grain size effects on nanocutting behaviour modelling based on molecular dynamics simulations

Grain size is one of the most critical factors affecting the mechanical and thermal properties of metallic materials. In this study the effect of the grain size of a workpiece made of pure Aluminium on the nanocutting process has been investigated via means of Molecular Dynamics simulations. The polycrystalline workpiece has been generated starting from a Face-Centred Cubic block of Aluminium atoms which was melted and subsequently quenched under various cooling rates in order to control the average grain size. The case of a monocrystalline workpiece has been considered as well. The generated workpieces were ground by a diamond abrasive. Simulations have been repeated in order to eliminate any statistical errors. The obtained results suggest that the average grain size of the workpiece significantly influences almost every aspect related to the nanocutting process. More specifically, it has been found that the cutting forces increase and the friction coefficient decreases with the grain size. Very small grain sizes lead to lower thermal conductivity and consequently high temperature at the cutting region. Finally, it has been shown that the high residual stresses at the grain boundaries can be relieved as the tool passes on top of the workpiece; this phenomenon resembles heat treatment. In summary, the nanocutting behaviour of polycrystalline materials depends on the average grain size and significantly differs from the case of monocrystalline materials. This should be taken into account in future numerical models of nanocutting processes.

Study on the crack formation mechanism in nano-cutting of gallium arsenide

Gallium arsenide is a typical brittle material, and crack formation is one of the most serious issues in the nanometric processing. This paper majors in studying crack formation mechanism in nano-cutting of gallium arsenide. In the molecular dynamics simulation of nano-cutting process, the main damage changes from dislocation to phase transformation with the increasing cutting speed. The amount of cracks increases with the higher cutting depth, and the deformation mode turns from ductile to a combination of ductile and brittle. Cracks appear at the boundary between amorphous layer and single crystal in the subsurface and tensile stress concentration is observed around the crack tip. The crack area is polycrystalline in the models with large tool radius. Brittle-ductile transition is observed by taper-cutting experiment of gallium arsenide, and the cutting depth is measured as 25 nm where the initial surface crack forms, which proves the low brittle-ductile transition depth of gallium arsenide. Micro cracks and polycrystals are found in the subsurface of transition area by cross section TEM, which is consistent with simulation results.

Research on the nanocutting mechanism of Ni-Fe-Cr-based superalloys: Conventional cutting versus UEVC

To compare the nanocutting mechanisms using conventional cutting and ultrasonic elliptical vibration cutting (UEVC) of Ni-based superalloys, molecular dynamics simulations were used to simulate the nanocutting process. The effects of ultrasonic vibration frequency and phase angle on the material removal rate of workpieces under UEVC were investigated. The results showed that von Mises stress concentration occurred at grain boundaries under both conventional cutting and UEVC, although this concentration was more distinct under UEVC. At a higher ultrasonic vibration frequency, the material removal rate increased, and the surface quality of the workpiece was improved. 1/6<112>Shockley dislocations were the primary dislocation form of nanocutting, while dislocations with an unknown structure were the secondary form. The ultrasonic vibration frequency and the phase angle affected the 1/6<112>Shockley dislocation density in a fairly complex manner. At ultrasonic vibration frequencies lower than 100 GHz, the 1/6<112>Shockley dislocation density first increased and then decreased in all cases, but at ultrasonic vibration frequencies greater than 200 GHz, the 1/6<112>Shockley dislocation density first decreased and then increased in all cases. Overall, the coordination numbers displayed a normal symmetrical distribution centered at about 49.

Investigation of the Subsurface Temperature Effects on Nanocutting Processes via Molecular Dynamics Simulations

In this investigation, three-dimensional molecular dynamics simulations have been performed in order to investigate the effects of the workpiece subsurface temperature on various nanocutting process parameters including cutting forces, friction coefficient, as well as the distribution of temperature and equivalent Von Mises stress at the subsurface. The simulation domain consists of a tool with a negative rake angle made of diamond and a workpiece made of copper. The grinding speed was considered equal to 100 m/s, while the depth of cut was set to 2 nm. The obtained results suggest that the subsurface temperature significantly affects all of the aforementioned nanocutting process parameters. More specifically, it has been numerically validated that, for high subsurface temperature values, thermal softening becomes dominant and this results in the reduction of the cutting forces. Finally, the dependency of local properties of the workpiece material, such as thermal conductivity and residual stresses on the subsurface temperature has been captured using numerical simulations for the first time to the authors’ best knowledge.

Molecular dynamics simulation on structure evolution of silica glass in nano-cutting at high temperature

ABSTRACT Machining of silica glass is indeed a challenge due to its extreme brittleness and hardness. In recent years, laser-assisted machining (LAM) is becoming a powerful method for cutting silica glass. However, as a typical non-crystalline structure, the deformation mechanism of silica glass in the cutting process at high temperature has not been explored clearly. In this paper, classical molecular dynamics simulation was conducted to investigate the structure evolution of silica glass during the nano-cutting process at high temperature. Firstly, a uniaxial tension test was carried to investigate the brittle-to-ductile transition with increasing temperature. Then, the cutting simulation was conducted at 300 and 1500 K. The results showed that the plastic deformation is promoted at 1500 K. The atomic flow of silica glass is different from crystal material during the cutting process. No rotational flow and upward motion of atoms are observed. Moreover, microstructure evolution like bond-switch and rings distribution was discussed in detail. Furthermore, although the densification scope is almost unaffected, the extent of densification near the machined surface is greatly decreased at a high temperature. These results contribute to the theoretical research on the precision machining of silica glass with LAM.

Multiscale Assessment of Nanoscale Manufacturing Process on the Freeform Copper Surface.

The nanocutting has been paid great attention in ultra-precision machining and high sealing mechanical devices due to its nanometer level machining accuracy and surface quality. However, the conventional methods applicable to reproduce the cutting process numerically such as finite element (FE) and molecular dynamics (MD) are challenging to unveil the cutting machining mechanism of the nanocutting due to the limitation of the simulation scale and computational cost. Here a modified quasi-continuous method (QC) is employed to analyze the dynamic nanocutting behavior (below 10 nm) of the copper sample. After preliminary validation of the effectiveness via the wave propagation on the copper ribbon, we have assessed the effects of cutting tool parameters and back-engagement on the cutting force, stress distribution and surface metamorphic layer depth during the nanocutting process of the copper sample. The cutting force and depth of the surface metamorphic layer is susceptible to the back-engagement, and well tolerant to the cutting tool parameters such as the tool rank angle and tool rounded edge diameter. The results obtained by the QC method are comparable to those from the MD method, which indicate the effectiveness and applicability of the modified QC method in the nanocutting process. Overall, our work provides an applicable and efficient strategy to investigate the nanocutting machining mechanism of the large-scale workpiece and shed light on its applications in the super-precision and high surface quality devices.

Effects of cutting parameters on the subsurface damage of single crystal copper during nanocutting process

In order to explore how cutting parameters affect the evolution of subsurface defect of single crystal copper during nanocutting process, a nanocutting model is constructed based on LAMMPS; the nanocutting process of single crystal copper is investigated through molecular dynamics (MD) simulations for different cutting speeds and cutting depths, using EAM potential between Cu atoms and Morse potential between Cu atoms and the tool atoms. The results show that at the same cutting depth, cutting speed does not make much difference to the subsurface dislocation form; at the same cutting speed, cutting depth makes a great difference to the subsurface dislocation form and it also affects the crystal structure type of the defect layer very significantly. Under any cutting parameters, the dislocation form of 1/6<112> is dominant. With the increase of cutting speed and cutting depth, the dislocation of 1/6<110> and 1/3<100> of subsurface layer increased obviously, and the length of dislocation line also increased.

Nanocutting mechanism of 6H-SiC investigated by scanning electron microscope online observation and stress-assisted and ion implant-assisted approaches

Nanocutting mechanism of single crystal 6H-SiC is investigated through a novel scanning electron microscope setup in this paper. Various undeformed chip thicknesses on (0001) orientation are adopted in the nanocutting experiments. Phase transformation and dislocation activities involved in the 6H-SiC nanocutting process are also characterized and analyzed. Two methods of stress-assisted and ion implant-assisted nanocutting are studied to improve 6H-SiC ductile machining ability. Results show that stress-assisted method can effectively decrease the hydrostatic stress and help to activate dislocation motion and ductile machining; ion implant-induced damages are helpful to improve the ductile machining ability from MD simulation and continuous nanocutting experiments under the online observation platform.

Study on surface generation in nano-cutting by large-scale molecular dynamics simulation

Large-scale molecular dynamics simulations are employed in investigating the nano-cutting process. A cutting tool with 1-μm nose radius and 20-nm edge radius is applied in nano-cutting of silicon with cutting distance attaining 400 nm. The mentioned cutting parameters are relatively larger than those used in the former research studies which would help to obtain the results with relatively high confidence coefficient. The results show that when the UCT is smaller or similar to the stagnation height, the extrusion accompanied with the side flow dominates the material removal mechanism. The generated side flow will deteriorate the generated surface roughness. When cutting at {111} direction, bct5-Si phase forms and a part of them is left in the machined subsurface. When cutting at {100} direction, the formed bct5-Si and S-II phases transform to the a-Si phase, when the cutting tool passes through.

Improving nanocutting surface quality by force-controlled rolling

Force-controlled rolling method which is a combination of rolling tool, force sensor and fast tool servo is proposed to realize real-time control of rolling force in surface modification process. Especially when the surface is complex, the rolling force can be changed dynamically based on the surface profile and the rolling path. Therefore, the machinability of soft material, such as lead (Pb), are easy to be modified by force-controlled rolling. After the soft and sticky workpiece, lead, is modified, the surface of it becomes hard enough to suppress the scratch of the chips, the formation of built-up edge, and the side flow of the workpiece material at the subsequent nanocutting process. Nanocutting of Pb mirrors validates the effectiveness of the force-controlled rolling method. Besides that, side flow region under the action of the tool edge and its evolution after the formation of build-up edge is investigated.

Effect of dynamic adjustment of diamond tools on nano-cutting behavior of single-crystal silicon

A new method for adjusting the tool rake and flank angles by changing the position of the tools was used to dynamic explore the nano-cutting behavior of single-crystal silicon using MD simulation. Simulations under the same cutting conditions were carried out using a tool swinging to six different rake angles of − 10°, − 15°, − 20°, − 25°, − 30°, − 35°, and − 45°. The advantages of Tersoff potential function are discussed in comparison with those of using SW potential function. The coordination number, von Mises stress, hydrostatic stress, system temperature, potential energy and cutting force during the nano-cutting process are studied. The results of a statistical study reveal that the coordination numbers of silicon atoms showed a minimum value and the highest average hydrostatic stress at − 25° adjustment angle. Besides, the maximum system potential energy and temperature is also obtained at an adjustment angle of − 25° after − 20° (it can be defined as a larger adjustment angle after − 15°). In addition, the results also point out that the highest average tangential force was observed at − 25°, which is different from the previous researches.

Investigation of Nanocutting Characteristics of Off-Axis 4H-SiC Substrate by Molecular Dynamics

Silicon carbide (SiC), especially 4H-SiC, is an ideal semiconductor in power electronics due to its outstanding electrical and thermal properties. It has high hardness and brittleness, which makes it difficult to machine. To understand the nanomachining characteristics of off-axis 4H-SiC and provide suggestions on 4H-SiC substrate thinning, the nanocutting process of 4 ∘ off-axis 4H-SiC was simulated by molecular dynamics. The results showed that the stacking fault induced by cutting propagates in the basal plane, and propagates deep into the SiC workpiece when the angle between the cutting direction and the c-axis is smaller than 90 ∘ . Bond reconstruction is found near the slip plane. The cutting depth is also a key parameter in nanocutting. With smaller cutting depth, machining is more like scratching than cutting. With larger cutting depth, more atoms are involved in the cutting, cutting force and workpiece temperature are higher, and more defects exist.

Influence of tool rotation on 3D surface topography at the nanometric scale

ABSTRACTThe influence of the tool rotation on the 3D surface topography produced by the nano-cutting process is investigated using molecular dynamics simulations. The least square mean method is utilized to model the evaluation criteria for the surface roughness parameters. The effects of the tool rotation on the cutting force and the chip formation at the nano-metric scale are also evaluated. It is found that the chip formation produced with tool rotation is dominated by the ploughing and the shearing forces. With increase of the adopted rotation velocity, the cutting force is sharply increased and the smaller elastic recovery of the machined surface is observed. The 3D surface roughness parameters at the nano-metric scale are significantly influenced by the tool rotation velocity and the feed speed, and the surface quality can be improved by decreasing the tool rotation velocity and the feed speed.

A numerical study on the material removal and phase transformation in the nanometric cutting of silicon

The mechanism of material removal process at the nanoscale lays the foundation for nanomachining technology. There are two major material removal mechanisms in cutting: extrusion and shear. Though the shear theory has been successful in describing the conventional macro cutting methods, it may not be suitable for understanding the material removal at the nanoscale. As an alternative, the extrusion model was proposed for nanometric cutting. However, the concept of extrusion remains ambiguous, and the differences between extrusion and shear have not been fully clarified. In this research, molecular dynamics is performed to study material removal under various cutting conditions. Novel analysis methods are developed to characterize the nanocutting process for numerical simulation. The fundamental processes of extrusion and shear are successfully revealed. Chip formation and subsurface damage evolution are clearly interpreted. In addition, the variation in material removal with the sharpness of the cutting tool is analyzed. The results are significant for the development of the cutting theory.

Effects of recovery and side flow on surface generation in nano-cutting of single crystal silicon

The effects of the recovery and side flow on the surface generation, as well as the stagnation region, phase transformation in nano-cutting of single crystal silicon are investigated by means of molecular dynamics. In this study, the workpiece material would experience two cutting processes in the conditions where the recovery and subsurface damage of the former cutting trace could be and not be taken into consideration. Therefore, the combined effects of the side flow and recovery on the surface generation are decoupled and investigated respectively. The results show that the side flow of the material increases the generated surface roughness making it deviate from the theoretical value. The recovery left on the former cutting trace enlarges the size of side flow and further increases the surface roughness indirectly. But the overall surface roughness is decreased by the effect of recovery. Comparing the effects of the side flow and the recovery on the generated surface roughness, the side flow plays a more important role in surface generation of nano-cutting process. Therefore, the suppression of the side flow is an effective way to improve the generated surface roughness in nano-cutting. The phase of single crystal silicon in machined subsurface is transformed to amorphous and bct5-Si phases. A larger stagnation height would make more materials phase transformed.

Study on machinability of silicon irradiated by swift ions

Diamond cutting of hard and brittle materials is difficult owing to poor surface quality and severe tool wear. It has been clear that ion implantation can be used to improve the machinability. In previous studies, surface modification is realized by the nuclear collision cascade that induces phase transition during the implantation. Except for the nuclear collision process, electronic interaction between the incident particles and the target material, such as ionization, also occurs particularly during a high-energy ion implantation. However, the influence of ionization on the machinability has not been studied. In this paper, modification on the nanocutting of silicon by MeV oxygen ions is studied. Molecular dynamics simulation is conducted to reveal the nanocutting process on silicon with irradiation damages. Experiments show an enhancement in the critical undeformed chip thickness that is crucial in machining of brittle materials.

A study on the tool edge geometry effect on nano-cutting

The tool edge has a significant influence on a cutting process especially when it is comparable to uncut chip thickness. Generally, the cutting tool edge is considered rounded and is characterized by a tool edge radius. When the cutting tool edge geometry is not a symmetrical circle, the tool edge radius fitted with the former methods is not sufficient to describe the performance of the cutting edge. In this study, a parameter, which is different from the previous description method, is proposed to characterize the tool edge. Three different tool edges are reconstructed to investigate the effect of the proposed parameter on a nano-cutting process using molecular dynamics. Results show that combined with the former used tool edge radius, the newly proposed tool edge characterization parameter which is the tool edge radius fitted with the edge profile at the flank face side could be used to characterize the cutting performance of an asymmetric tool edge. The minimum uncut chip thickness, subsurface damage, and cutting force in feed direction investigated in this study tend to increase with the newly proposed characterization parameter. A stagnation region formed in front of the cutting edge acts as a new formed cutting edge making the material removed in shearing mechanism when the uncut chip thickness is larger than the minimum uncut chip thickness. However, when it is similar or smaller than minimum uncut chip thickness, the stagnation region is not tough enough to cut the materials making it to slide on the surface and part of the atoms in the upper layer of workpiece is removed by extrusion. Two models are proposed to describe the shearing and extrusion mechanism in a nano-cutting process.

A study on the surface quality and brittle–ductile transition during the elliptical vibration-assisted nanocutting process on monocrystalline silicon via molecular dynamic simulations

Molecular dynamic (MD) simulation was applied to investigate surface quality and brittle–ductile transition of monocrystalline silicon with a diamond tool during elliptical vibration-assisted nanocutting (EVANC) and traditional nanocutting process.